1. Field of the Invention
This invention relates to naphthenohydroxamic acid, its preparation and use in hydrometallurgical processes to recover metal values and more particularly in liquid ion exchange processes.
2. Description of the Prior Art
U.S. Pat. No. 2,397,508 - G. F. Rouault and H. D. Rhodes, issued Apr. 2, 1946, describes preparation of naphthenohydroxamic acid from an ester of naphthenic acid by adding a dry hydroxylammonium salt such as the sulfate or chloride to the neutralized ester in alcohol and adding an aqueous sodium hydroxide solution to liberate the free hydroxylamine and convert the ester to the hydroxamic acid. The procedure is lengthy and yields are low.
U.S. Pat. No. 2,818,429 - Beretvas issued Dec. 31, 1957, describes an improved procedure for manufacture of naphthenohydroxamic acid from an ester of naphthenic acid by dissolving hydroxylammonium chloride in alcohol, adding the ester to the alcohol solution and neutralizing with an aqueous sodium hydroxide solution. The critical factors in this procedure are claimed to be: (1) the hydroxylammonium salt must be dissolved in alcohol; and (2) the amount of water in the reaction mixture must be not more on a weight basis than the amount of sodium hydroxide used.
This procedure is an improvement over the preparation described in U.S. Pat. No. 2,397,508 but it has two major disadvantages:
1. About one-third of the ester is decomposed because the saponification reaction is competing with the conversion of the ester to hydroxamic acid reaction. This is the result of addition of a water solution of metal hydroxide during the critical stage of the reaction when the ester is being converted to hydroxamic acid.
2. The most inexpensive source of hydroxylamine is hydroxylammonium sulfate, not hydroxylammonium chloride, which increases cost of the free base 2-3 times. The sulfate cannot be used in the process of U.S. Pat. No. 2,818,429 because it is completely insoluble in alcohol.
Hydrometallurgical processes for the treatment of ores and concentrates especially in the recovery of copper and nickel have been known to the mining industry for the last two decades. Some 15% of the copper produced in the United States is now produced by hydrometallurgical techniques and production of nickel from laterites is becoming standard practice through the world. The most important hydrometallurgical commercial process for copper employs substituted 2-hydroxybenzophenoximes. See, e.g., U.S. Pat. No. 3,428,488 - Swanson issued Feb. 18, 1969. This process involves extraction of copper from dilute leach solutions by a countercurrent process using a water insoluble organic solvent solution of the chelating agent to form a metal complex. The so formed metal complex remains dissolved in the organic phase at a much higher concentration than originally present in the leach solution. Recovery of copper is accomplished by stripping the organic phase with a strong (10-30%) sulfuric acid solution.
The principal disadvantages of processes using substituted 2-hydroxybenzophenoneoximes are the relatively high cost of the chelating agent, its low chelating capacity and the very strong acid required for stripping. The strong acid causes gradual deterioration of the capacity of the chelating agent.
U.S. Pat. No. 3,367,959, Fetscher and Lipowski, issued Feb. 6, 1968, discloses the preparation and use of oil soluble chelators which are amidoximes and hydroxamic acids containing ester moieties. These materials are expensive to prepare and because of the presence of the ester linkage tend to decompose under acid conditions.
There is a need for further improvements in chelating agents as well as in hydrometallurgical processes where these agents are to be used. If naphthenohydroxamic acid is to be useful as a chelating agent in metal recovery processes, it is important to obtain a product having the maximum chelating capacity; e.g., complete conversion of the ester group to a hydroxamic acid group which contains the chelating oxime moiety, -C=N-OH.